There has been, for example, described a conventional composite device exhibiting antifouling property and hydrophilicity manufactured by depositing, on a base surface, a photocatalytic titanium oxide film, on which a porous inorganic oxide film (e.g., silica) is deposited (Japanese Patent Laid-Open No. 10-36144).
In the above conventional composite device, the photocatalytic titanium oxide has a high refractive index n (n=about 2.4), leading to high surface reflection on the device surface. Thus, when applied to, for example, an automobile rear view mirror, it may cause a double image. Furthermore, when the photocatalytic titanium oxide film is thick, it may cause interference colors.
This invention, therefore, is directed to provision of a composite device by which the problems in the above-mentioned prior art can be solved, i.e., surface reflection and interference colors can be minimized, photocatalytic decomposition performance can be improved and a hydrophilicity-acquiring rate can be improved.